I remember being very nervous but I want to do it for personal progression. I played the song too fast and stopped at one stage, then on a second attempt through nerves I forgot the words to the song which I know backwards and on top of that I gave myself a friction burn on my strumm fingers when I hit the strings. Would I do it again... absolutely.
Since then I have had several opportunities to step up but have declined and afterward I have been disappointed in myself. I know I can play, I'm not so confident about my voice but my friends have said I sing fine but I am getting in my own way.
My advice is to go for it, you only live once and we all make errors but thats how we learn [I'm going to read this and follow my own advice next time the opportunity arises]... Best of luck all.